That #NeverTrump candidate just might pull more votes away from the Democrat than Trump.
Usually, the strongest 3rd-party or independent presidential candidate takes votes from the incumbent party. In 2000, when the president was a Democrat, Ralph Nader got about 3%, helping Bush win. In 1992, when Bush ran for re-election, Ross Perot got about 19%, helping Clinton win. In 1968, when the president was a Democrat, George Wallace got 46 electoral votes, helping Nixon win.